Can I compost tomato plants killed by late blight?

I just got this article from Dr. Beth Guigino, our vegetable pathologist at Penn State. Dr. Meg McGrath, form Cornell University also contributed. I thought it would help a lot of our home gardeners who are cleaning up their beds this fall!

Can plants with late blight be disposed of by composting?

If done correctly, it can. Proper composting involves going through both the active and curing phase of composting where the temperature reaches specified temperatures for lengths long enough to kill pathogens and weed seed. If done incorrectly, some plant tissue, like potato tubers, can survive in the center of a warm compost pile. As long as the infected plant tissue is alive, the pathogen can survive. Tomato plants and fruit will not survive a Pennsylvania winter in a compost pile, so it is safe to add them.

Late blight can survive in infected potato tubers overwinter and can be a potential source of the disease the next year.Therefore, don't put infected tubers in a compost pile. It is best to dispose of them in the regular trash. Another option would be to chop-up infected tubers and spread them on the soil surface so they freeze overwinter thus killing both the plant tissue and late blight pathogen. Next season it will be important to destroy all volunteer tomato and potato plants. Guidelines have been developed on composting cull potato tubers for commercial operations:< http://www.umaine.edu/umext/potatoprogram/Fact%20Sheets/Composting%20Cull%20Potatoes.pdf >.

Do I need to treat the soil this fall to prevent late blight from developing next year?

No. The late blight pathogen is an obligate pathogen and thus requires living plant tissue to survive overwinter. Once the tomato plant tissue is dead, the pathogen cannot survive on the crop debris like many other vegetable pathogens. The specialized overwintering survival structure (oospore) of the late blight pathogen requires two mating types (equivalent to male and female) to go through sexual reproduction and form. To our knowledge, there is only one mating type in Pennsylvania and the Northeast. Without the compatible mating type, no oospores form and, therefore, there is no risk of this season's late blight surviving in the soil and being a source of the disease next season.

Can the late blight pathogen survive in or on tomato seed?

No. Fortunately this pathogen is not able to get inside the seed and it does not produce a type of spore that is able to survive on the outside of the seed. Thus there is no concern that late blight will develop as a result of growing plants next year from seed that were in tomato fruit infected with late blight. There are other pathogens (especially bacterial pathogens) that can survive in and/or on seeds, thus there are other reasons to only use seed from healthy plants.

Could the late blight pathogen survive on tomato cages and stakes between seasons?

No. It is not necessary to discard or even disinfect the cages or stakes to manage this disease. It is a good idea, however, to disinfect stakes and cages to help control bacterial diseases (bacterial spot, bacterial speck and/or bacterial canker). These bacterial pathogens can survive overwinter in the cracks and crevices and be a source of the disease next season. Disinfectants include: quaternary ammonium chloride salts (e.g., Green-Shield), sodium hypochlorite (Clorox or other household chlorine bleach 5.25%, so use 0.5% = 1 part bleach + 9 parts water), and hydrogen dioxide (e.g., Oxidate). Clean off soil and organic matter first because this inactivates disinfectants and can protect pathogens that are inside. This is especially important when using bleach. Soak at least ten minutes. Disinfectant solution can be reused until it becomes dirty or ineffective (replace Green-Shield after 24 hours; the half-life for bleach is only two hours).

Are there late blight resistant tomato varieties that I should consider planting in the future?

Currently, there are some potato varieties described as having some resistance. These include 'Elba', 'Kennebec', 'Allegany', 'Sebago', 'Rosa', 'Defender', 'Jacqueline Lee' and 'Ozette'. 'Elba' is considered the most resistant. There are some tomato varieties in the final stages of development and are expected to be available as soon as 2010.

Current Comments

i have read on line that half life chlorine bleach solution 2 hrs.i cannot find info on half life acidified household bleach at ph 5 or6. would it be about two hours as well? thankyou for your time

Posted By: regt | Jan 21, 2010 7:47:41 PM

I had late tomato blight, live in McKean Co , PA and would like to know what plants are best to utilize this year in my garden. I'm particularly interested in these: Herbs? Lettuce (and salad type garden), and tomatoes? I usually grow from seed, but have purchased at local greenhouse, Walmart, and Home Depot. I'm thinking of transferring my herb garden into the garden that had the tomato blight. Will I ever be able to plant tomatos in the same area I had the blight (mine came very late, we thought it missed us at first, then suddenly everthing turned). Thank you.

Posted By: E | May 3, 2010 12:30:54 PM

I had heard that the tomato blight came from the big box stores, Walmart, Home Depot, & Lowes. The reason being they brought it up to the North from the South. Seem like it would be better to buy from a local nursery that grow on sight, if you can find one these days. If this is true does anyone know of safeguards that have been put into place?

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Master Gardeners are volunteers trained by Penn State Extension Horticulture Educators. Once they complete their training, they cooperate with service agencies and community groups on a wide range of gardening projects. Their talents and energies are directed toward providing a link between their community and Penn State Cooperative Extension and Outreach.